492 



NATURE 



[March 23, 189^ 



in muscle and nerve in all its characters, and, at the end of his 

 work, had also disclosed the inadmissibility of vital force, then 

 the venerable Humboldt formally and expressly renounced the 

 ■dream of his youth, with the masterly submission of the true 

 naturalist to the recognised natural law. 



The hypotheses of a particular force of life had, however, in 

 regard to Brown's theory neither a positive nor a negative value. 

 Johannes Miiller rescued for general physiology, in which it has 

 ever since kept its place, that which was valuable in Brown's 

 system, the doctrine of the integrating life stimuli. The occa- 

 sional stimuli which produce disease have found their place in 

 etiology ; their significance has become more and more sharply 

 defined, the more accurately we have learnt to distinguish 

 between the causes and the essences of disease, a distinction 

 which became more difficult as the "causae vivse " of diseases 

 became known in ever-increasing numbers. And now a new task 

 has arisen, namely, to draw into our sphere of observation the 

 life of the causative agents themselves. 



The way in which pathology has tried to approach the desired 

 goal, to fathom the living substance in its diseased conditions, 

 has led us a great step forward. Pathological anatomy, es- 

 pecially, has opened this road. The more numerous its observa- 

 tions, and the more it penetrated into the details of the lesions, 

 the smaller became the field of so-called general diseases. The 

 first steps of medieval anatomists had the effect of drawing the 

 attention to local diseases. In the first and longest period, 

 which one may define as that of Regionism, the pathological 

 anatomists sought the cause of disease in one of the larger 

 regions or cavities of the body — in the head, chest, or abdomen. 

 In the second period, ushered in by the immortal work of Mor- 

 gagni, shortly before the time of which I last spoke — the time of 

 Brown and Hunter — they endeavoured to find in a certain 

 region the actual organ which might be considered as the seat of 

 disease. On this foundation arose the Parisian school of Or- 

 ganicism, which, until late in this century, held a dominant 

 position in pathology. In this school, already, they recognised 

 that not the organ, nor even a portion of it, could be the ultimate 

 object of research. Xavier Bichat divided the organs into 

 tissues, and showed that in the same organ sometimes one and 

 sometimes another tissue might be the seat of disease. 



From that time forward the eye of the pathological anatomist 

 was directed chiefly to the changes in the tissues, but it soon 

 became apparent that even the tissues are not simple substances. 

 Since the third decade of this century, the microscope has dis- 

 closed the existence of cells, first in plants, and very soon after- 

 terwards in animals. Only living beings contain cells, and 

 vegetable and animal cells show so much similarity of structure 

 that one can demonstrate in them the actual product of organi- 

 sation. This conviction has become general, since through our 

 embryologists, especially through Schwann, proof has been 

 afforded that the construction of embryonic tissues was derived 

 from cells also in the highest animals and in man himself. 



In the fourth decade of this century the science of patho- 

 logical anatomy had already begun to be directed tcwards cells. 

 These lesearches very soon struck on great difficulties. Many 

 tissues, even in their developed state, appeared to contain 

 neither cells nor their equivalents ; nevertheless, I have been 

 able to demonstrate their existence in those tissues in which 

 their presence appeared to be most doubtful, viz. in bone and 

 connective tissues. At the present time we are so far advanced 

 as to be able to say that every living tissue contains cellular 

 elements. We go a step further even, for we require that no 

 tissue should be called living in which the constant occurrence 

 of cells cannot be shown. 



A still greater difficulty then appeared, namely, to discover 

 in what way new cells originated. The answer to this question 

 had been very heavily prejudiced by the so-called cell-theory of 

 Schwann. Inasmuch as this very trustworthy investigator 

 asserted that new cells originated from unformed matter, from 

 " cyto-blastema," there was opened up a wide road to the old 

 doctrine of the "generatio ajquivoca," which afforded all parti- 

 sans of plastic materials an easy way of reviving their dogma. 

 The discovery of cells of connective and allied tissues gave me 

 the first possibility of finding a cellular matrix for many new 

 growths. One observation followed another, and I was soon 

 in a position to give utterance to the dictum, " Omnis cellula a 

 cellula." 



And so at last the great gap was closed which Harvey's ovistic 

 theory had left in the history of new growth, or, to speak more 

 generally, in the history of animal organisation. The begetting 



NO. 122 I, VOL. 47] 



of a new cell from a previous cell supplements the reproduction 

 of one individual from another, of the child from the mother. 

 The law of the continuity of animal development is therefore 

 identical with the law of heredity, and this I now was able to 

 apply to the whole field of pathological new formation. I 

 blocked for ever the last loophole of the opponents, the doctrine 

 of specific pathological cells, by showing that even diseased life 

 produced no cells for which types and ancestors were not forth- 

 coming in normal life. 



These are the fundamental principles of cellular pathology. 

 In proportion as they have become more certain, and more 

 generally recognised, they have in turn become the basis of 

 physiological thought. The cell is not only the seat and vehicle 

 of disease, but also the seat and carrier of individual life ; in it 

 resides the "vita propria." It possesses the property of irrit- 

 ability, and the changes in its substance, provided these do not 

 destroy life, produce local disease. 



Disease presupposes life ; should the cell die, its disease also 

 comes to an end. Certainly, as a consequence, the neighbour- 

 ing and even far distant cells may become diseased, but as re- 

 gards the cell itself the susceptibility to disease is extinguished 

 with life. 



Since the cellular constitution of plants and animals has been 

 proved, and since cells have become recognised as the essentially 

 living elements, the new science of biology has sprung up. It 

 has not brought us the solution of the ultimate riddle of life, but 

 it has provided concrete, material, anatomical objects for investi- 

 gation, the structures and active and passive properties of which 

 we can analyse. It has put an end to the wild confusion of 

 fantastic and arbitrary notions such as I have just mentioned ; it 

 has placed in a strong light the immeasurable importance of 

 anatomy, even-in the most delicate conditions of the body ; and 

 lastly, it has made us aware of the close similarity of life in the 

 highest and lowest organisms, and has thus afforded us invaluable 

 means for comparative investigation. 



Pathology has also its place, and one certainly not without 

 honour, in this science of biology, for to pathology we are in- 

 debted for the knowledge that the opposition between healthy 

 and diseased life is not to be sought in a fundamental difference 

 of the two lives, not in an alteration of the essence, but only in 

 an alteration of the conditions. 



Pathology has been released from the anomalous and isolated 

 position which it had occupied for thousands of years. By 

 applying its revelations not only to diseases of man, but also to 

 those of animals, even the smallest and lowest, and to those of 

 plants, it in the best manner helps to strengthen biological 

 knowledge, and to narrow still more that region of the un- 

 known which still surrounds the intimate structure of living 

 matter. It is no longer merely applied physiology ; it has be- 

 come physiology itselK 



Nothing has more contributed thereto than the constant 

 scientific union which has endured for more than 300 years 

 between English and German investigators, and to which we 

 to-day add yet another link. May this union never be broken ! 



APPLIED NATURAL HISTORY. 



T^HE so-called experimental sciences —chemistry and 

 ■*■ physics — in their various branches, have hitherto 

 been more extensively "applied" to the service of man, 

 than the observational sciences of botany and zoology. 



The various industries in which civilised man has 

 naturally become engaged have induced a scientific study 

 of the fundamental principles, and an eager search for 

 such inform.ation as can lead, with the assistance of art, 

 to a further advance towards the goal of perfection. 



It is true, however, that the practice of medicine has 

 much dependence on the science of botany. 



Zoology, on the other hand, has never been considered 

 as possessed of qualities serviceable to any bread-winning 

 occupation, and although included, like' botany, in all 

 ordinary courses of medical study, has not until recently 

 been considered of importance for the advancement of 

 any industry. 



Now, when the nineteenth century is in its last decade, 

 we in this country are beginning to realise that a know- 

 ledge of the life-histories and habits of sea-fishes and 



